Abstract: A color sensor includes a plurality of light emitting sources of different colors each of which is driven in a time divisional manner to emit the different colors sequentially, a light receiving element for receiving the light from an object illuminated by the respective color lights from the light emitting sources and a circuit arrangement for producing output signals representing the color of the object.

Abstract: A hexagonal NaLnF.sub.4 :Yb.sup.3.sup.+, Er.sup.3.sup.+ (Ln represents the elements Y, La, Gd and/or Lu) has been found to be an efficient phospor emitting green light with infrared excitation, which can be prepared by firing a mixture of Na.sub.2 SiF.sub.6 and coprecipitated Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.3. Optimum firing conditions for synthesis of NaLnF.sub.4 :Yb.sup.3.sup.+, Er.sup.3.sup.+ have been found to be such that:A. the decomposition reaction of Na.sub.2 SiF.sub.6 to (2NaF + SiF.sub.4) is complete,B. liquid NaF-Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.3 and hexagonal NaLn.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.4 are co-existent, andC. the hexagonal-to-cubic phase transition does not occur in NaLn.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.4.When pumped by a Si-doped GaAs diode, properly prepared NaY.sub.0.57 Yb.sub.0.39 Er.sub.0.04 F.sub.4 emit under infrared stimulation green light 4 to 5 times as bright as commercially available LaF.sub.3 :Y.sup.3.sup.+, Er.sup.3.

Abstract: An electro-optic ceramic material useful for electro-optic applications comprising an anti-ferroelectric phase (or para-electric phase) and a ferroelectric phase, the two phases of which coexist having a morphotrophic phase boundary. The scattering of light applied to the ceramic material can be changed by a voltage applied to the ceramic material whereby the anti-ferroelectric phase (or para-electric phase) and the ferroelectric phase are reversibly changed and thus the morphotrophic phase boundary is shifted corresponding to the phase changes.